Casting mold and method for casting achieving in-mold modification of a casting metal

ABSTRACT

A casting mold and method for its use to achieve in-mold modification of the casting metal is disclosed. One or more chambers are located within the casting mold&#39;s runner system. Each chamber can contain metallurgical modifiers for adjusting the chemical composition of the metal to improve the mechanical and physical properties of an article cast from the metal. One or more modifiers can be placed in the chamber(s) as the casting mold is assembled for use. As the melt is introduced to the casting mold, it passes through the chamber(s) and liquefies the modifier. Amounts of the liquid modifier, then, are carried away and become dispersed in the melt as it continues through the runner system and into the mold cavity. The metallurgical modifiers can be selected from any number of known additives or alloying elements, including strontium, among others.

FIELD OF THE INVENTION

The present invention relates to a casting mold and casting method forachieving in-mold modification of a casting metal, such as an aluminumalloy, by the addition of one or more metallurgical additives forimproving the mechanical and physical properties of the cast article.

BACKGROUND OF THE INVENTION

Cast metal articles are made at a foundry by introducing molten metalinto a mold from a relatively large volume of molten metal (i.e., amelt). It is well known to adjust the chemical composition of a castingmetal to improve the mechanical and physical properties of an articlecast from the metal. This is accomplished by the addition of one or moremetallurgical additives or modifiers.

Some additives or modifiers “modify” the way a cast material solidifies.The desired effects of the modifying material can be observed at themicroscopic or metallographic level. The size, shape and crystallinecomposition of the micro-constituents of the solidified alloy can beinfluenced through the addition of small amounts of “modifiers.” Thesemodifiers typically exhibit little or no “alloying” effect, in the sensethat they have negligible impact on the chemical composition of themelt. In this regard, the melt is modified by liquefying and dispersingthe modifiers in the melt, before it is used to fill a mold.

Molten aluminum can be alloyed by the addition of alloying elements.Common aluminum alloying elements include copper, iron, magnesium,manganese, nickel, silicon, tin, and zinc. These alloying elements aretypically added to the molten melt to formulate a specific aluminumcasting alloy. Modifying elements, alloys and compounds may also bedispersed in the aluminum melt. Such additives include antimony,beryllium, boron, calcium, phosphorous, silver, sodium, strontium,titanium, titanium boron, vanadium, zirconium, and other elements andcompounds of elements.

Strontium, in particular, is known to have a notable impact on thesilicon morphology, porosity distribution and porosity volume in acasting, positively influencing the mechanical properties and thefunctional aspects (e.g., leak prevention) of the cast article.

Metallurgical modifiers, including strontium, are conventionally addedto an aluminum melt in relatively small bricks, pellets or tablets thatare subsequently liquefied and dispersed in the melt. It is also knownto include these additives by moving an alloy wire into a stream of themolten metal. The introduction of the additives to the melt is typicallyperformed at the holding furnace, launder, or ladle and at apredetermined time prior to pouring the melt into the mold.

Control over the time that elapses between the introduction of themodifier to the melt and use of the melt is important because thedesired and beneficial effects of metallurgical modifiers that aredissolved in a melt diminish with the passage of time. This phenomenonis known as fade. Such degradation of the efficacy of the metallurgicalmodifier is an undesired result and reduces the effective concentrationof the metallurgical modifier in the aluminum melt. Consequently, tocounter the negative impact of fade, it is often the practice toover-treat the molten melt with strontium or other modifiers. Whendealing with the metallurgical modifier strontium, in particular, it isbelieved in the foundry industry that the modifying alloy of strontiummust be added to the melt before the metal is introduced to the mold sothat the strontium can disperse throughout the melt.

Foundry practices that improve both the manner in which metallurgicalmodifiers are introduced into the melt and their resultant effectivenessin enhancing the mechanical and physical properties of the cast article,therefore, continue to be sought.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a casting mold, such as is known insand casting processes, and a method for its use for achieving thein-mold modification of the casting metal. In addition to one or moremold components, such as a mold segment or a mold core, the casting moldgenerally includes the features of a sprue (also referred to as a moldinlet), through which the molten metal flows into the casting mold; arunner system having one or more channels that carry the molten metalfrom the sprue to the mold cavity; and one or more gates, that providethe inlets into the mold cavity from the runner system.

Included in the casting mold of the invention, however, is at least onechamber that is located within the casting mold's runner system. Thechamber is designed to contain metallurgical additives or alloyingelements for the purpose of adjusting the chemical composition of thecasting metal and improving the mechanical and physical properties of anarticle that is cast from the metal.

The modifiers can generally be provided as rod or bar stock or in agranular or pellet form. One or more such solid modifiers may be placedwithin the chamber as the casting mold is assembled for use. Uponintroduction of the molten melt to the casting mold, the melt liquefiesthe modifier as it passes through the chamber. Amounts of the liquidmodifier, then, are carried away, and become dispersed in the melt as itcontinues through the runner system and into the mold cavity.

The metallurgical additives can be selected from any number of knownmaterials specifically including, though not limited to, antimony,beryllium, boron, calcium, fluxing salts, phosphorous, silver, sodium,strontium, titanium, titanium boron, vanadium, and zirconium,individually or in combination.

In particular, the invention has the demonstrated capability for theaddition of strontium within the casting mold to an aluminum-siliconcasting melt. This is contrary to conventional wisdom in the foundry artand the typical practice of adding strontium to the entire metal melt atthe holding furnace.

The invention is flexible and it may accommodate any of a variety ofcasting molds and applications including, for example, single cavity ormulti-cavity casting molds.

The number of chambers and their physical configuration and location ina given casting mold may vary as desired or necessary, such as toaccommodate either a particular mold design or the requirements of anarticle to be cast. For example, the casting mold may include one ormore chambers at one or more specific locations within the runner systemin order to provide localized modification of the melt at specific areasin a cast article. Also, the invention contemplates that one or morechambers may be employed in a casting mold and each contain one or moremodifiers for adjusting the chemistry of the melt. As such, theinvention provides for the controlled distribution of metallurgicalmodifiers throughout a cast article.

The invention thus provides improved consistency and better control overthe mechanical and physical properties of articles cast in the mold,casting-to-casting and mold-to-mold. The invention simplifies theprocess of adding metallurgical modifiers, and reduces labor andmaterial costs that are associated with the continuous monitoring andmodification of an entire molten melt with modifiers. The invention alsominimizes the impact of fade on the modified melt.

Other benefits of the invention include reducing or eliminating theformation of sludge at the bottom of the holding furnaces caused by themodifiers. Such sludge negatively impacts the casting process bothclogging the electromagnetic metal pumps sometimes used to deliver themolten metal to the casting molds and resulting in inclusions in thecastings.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detaileddescription and the accompanying drawings. The components in thedrawings are not necessarily to scale, emphasis instead being placedupon illustrating the principles of the invention. Moreover, in thefigures, like reference numerals designate corresponding partsthroughout the different views.

FIG. 1 is a simplified cross-sectional view of a casting mold packagefor an engine block (without the end core) incorporating the invention;

FIG. 2 is an enlarged view of detail 2 of FIG. 1; and

FIG. 3 is an enlarged view of detail 3 of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

A precision sand casting process for casting articles from molten metalgenerally employs an expendable casting mold (also referred to as a moldpackage), such as one shown in the simplified cross-section of FIG. 1 at10, for example. The mold package 10 is assembled from various moldelements or components, typically made from resin-bonded sand. The moldcomponents are combined to form a cavity that defines the internal andexternal surfaces of the article to be cast.

Also included in conventional casting molds are other major moldfeatures including a sprue 12 (also referred to as a mold inlet) throughwhich the molten metal is introduced into the mold, a runner system 14comprising one or more channels that carry the molten metal from thesprue 12 to the mold cavity, one or more gates 16 that provide theinlets into the mold cavity from the runner system 14, risers (notshown) that supply additional metal to the casting to account forshrinkage during the solidification of the molten metal in the mold 10,and vents (not shown) to allow gases and air to escape from the mold 10as the molten metal enters.

For purposes of illustration and not limitation, the resin-bonded sandcores that are shown in FIG. 1 are for use in assembly of an enginecylinder block mold package to cast a V-type aluminum engine block. Theinvention is especially useful, although not limited to, assemblingcasting molds for precision sand casting of V-type engine cylinderblocks, although other configurations and parts may be cast with castingmolds according to the invention.

The mold package 10 is assembled from several resin-bonded sand coresincluding a base core 18, an integral barrel crankcase core (IBCC) 20having metal (e.g. cast iron, aluminum, or aluminum alloy) cylinder boreliners 22, two end cores (not shown), two side cores 24, two slab coreassemblies 26, a valley core 28, and a cover core 30. The coresdescribed above are offered for purposes of illustration and notlimitation as other types of cores and core configurations may be usedin the casting mold of the invention, depending upon the particulararticle to be cast.

The resin-bonded sand cores can be made using conventional core-makingprocesses such as a phenolic urethane cold box or Furan hot box where amixture of foundry sand and resin binder is blown into a core box andthe binder cured with either a catalyst gas and/or heat. The foundrysand can comprise silica, zircon, fused silica, and others. A catalyzedbinder can comprise Isocure binder available from Ashland ChemicalCompany.

Included in the casting mold 10 is at least one chamber 32 that islocated within the runner system 14. The chamber 32 is designed tocontain a metallurgical additive or alloying element 34 that is intendedto influence and beneficially adjust the chemical composition of thecasting metal to improve the mechanical and physical properties of thecast article.

The metallurgical additives or alloying elements 34 can be selected fromany number of known materials specifically including, though not limitedto, antimony, beryllium, boron, calcium, fluxing salts, phosphorous,silver, sodium, strontium, titanium, titanium boron, vanadium,zirconium, chrome, copper, iron, magnesium, manganese, nickel, silicon,tin, and zinc, or a combination of these materials. In particular, theinvention has proved useful for the in-mold addition of strontium to amelt of a 319 aluminum silicon alloy.

FIG. 1 shows at least portions of the runner system 14 and gates 16 ofthe casting mold 10. As shown in FIG. 1, the runner system 14 includesseveral chambers that contain a metallurgical modifier. A first chamber32 is shown near the sprue or mold inlet 12. Additional chamber(s) mayalso be included, such as further downstream in the runner system 14near a gate 16 (see FIG. 3, chamber 36).

Of course, the number of chambers and their physical configuration andlocation in a given casting mold may vary as desired or necessary, suchas to accommodate either a particular mold design or the particularmetallurgical requirements of an article that is to be cast. Forexample, the casting mold may include one or more chambers at one ormore specific locations within the runner system in order to providelocalized modification of the melt at specific areas in a cast article.Also, the invention contemplates that one or more chambers may beemployed in a casting mold and contain one or more modifiers foradjusting the chemistry of the melt. As such, the invention provides forthe controlled distribution of metallurgical modifiers throughout a castarticle.

In this regard, the invention is flexible and it may accommodate any ofa variety of casting molds and applications including, for example,single cavity or multi-cavity casting molds.

Referring to FIG. 2, an enlarged detail view of chamber 32 is shown. Asshown, the boundary of the chamber is defined as two different moldcores, the cover core 30 and the valley core 28, come together as themold package 10 is assembled. Of course, the chamber 32 may be locatedentirely within a single mold core, or it may be created by the assemblyof more than two mold cores, as desired or necessary to accommodate thecasting mold design incorporating the invention.

Within the chamber 32 is a metallurgical modifier 34. The metallurgicalmodifier 34 comprises a solid metal, for example, rod or bar stock.Additionally the modifier 34 may take the form of pellets or granules.An exemplary modifier 34 that has proven useful in modifying analuminum-silicon melt cast in a mold of the invention is a 5%strontium-containing alloy in the form of stock material, though it iscontemplated that about a 3% to about a 15% strontium-containing alloymay be used. Examples of stock sizes that may be used include a ⅜ inchdiameter Ti B Sr 6 rod, a 1 inch square “Castcut” bar, or a ⅞ inchdiameter “Quicksol” bar, or a ⅜ in diameter rod.

When the mold components are assembled into the casting mold, themodifier 34 is placed in the chamber and becomes part of the castingmold package 10.

Positioned in the runner system 14 downstream of the modifier 34 andadjacent to the exit from the chamber 32 is a silicon carbide coatedfoam filter 38. As shown in FIG. 2, two such filters 38 are includedbecause there are two exits downstream of the chamber 32. Consequently,the melt passes through the filter 38 as it continues through the mold10. These filters 38 are commercially available, for example from SELEE®corporation or Foseco International Ltd. In addition to filteringparticulates from the melt, the filters 38 aid in controlling the flowof the melt through the chamber 32 to ensure that the melt fills thechamber 32 and flows over and around the modifier 34. This isparticularly important for the initial portion of the melt when it isfirst introduced to the casting mold 10.

After the mold package 10 is assembled, the molten metal, e.g. analuminum alloy at a temperature above 1250° F., is introduced into themold through the sprue 12. The aluminum melt flows from the sprue 12into the runner system 14 and the chamber 32. As the melt fills thechamber 32, it flows over and around the modifier 34. As it does so, themodifier 34 slowly dissolves in the melt. The melt then passes throughthe filters 38 at the downstream ends of the chamber and eventually intothe mold cavity. Because the modifier 34 dissolves in the melt overtime, the modifier 34 is introduced to the entirety of the melt thatpasses through the chamber 32, improving the properties of the castmetal as it does so.

As shown in FIG. 3, a chamber 36 is located near a gate 16 of thecasting mold 10. Filters 38 retain a metallurgical modifier 40 that isin granular or pellet form. As previously described, when the meltreaches the chamber 36, it dissolves the modifier 40 and affects thechemistry of the melt. In this example, the effects of the modifier 40are localized to the portion of the mold cavity that is fed by the gate16 nearest the chamber 36.

It can be readily appreciated that the number of chambers included inthe casting mold, their respective sizes, shapes and locations in therunner system (e.g., at or near one or more of the mold gates or at ornear the mold inlet), as well as the types and amounts of metallurgicalmodifiers that are incorporated in the casting mold, may modified asnecessary to accommodate the design of any particular casting mold orthe particular metallurgical requirements for the article being cast.

This description of the invention is merely exemplary in nature and,while various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that other embodimentsand implementations are possible that are within the scope of thisinvention. Accordingly, the invention is not restricted except in lightof the attached claims and their equivalents.

1. A casting mold comprising: at least one mold elements; a sprue; arunner system comprising at least one channel; at least one gate; atleast one chamber located within the runner system and containing ametallurgical modifier.
 2. The casting mold of claim 1 wherein themetallurgical modifier is selected from the group of antimony,beryllium, boron, calcium, fluxing salts, phosphorous, silver, sodium,strontium, titanium, titanium boron, vanadium and zirconium, or acombination thereof.
 3. The casting mold of claim 1 wherein themetallurgical modifier is strontium.
 4. The casting mold of claim 3wherein the metallurgical modifier is about a 3% to about a 15%strontium-containing alloy in the form of stock material.
 5. The castingmold of claim 2 wherein the metallurgical modifier is in the form of barstock or rod stock material.
 6. The casting mold of claim 2 wherein themetallurgical modifier is in granular form.
 7. The casting mold of claim2 wherein the metallurgical modifier is in pellet form.
 8. The castingmold of claim 1 comprising a plurality of mold cores and wherein thechamber is bounded by at least two mold cores.
 9. The casting mold ofclaim 1 wherein the chamber is located at or near the at least one gate.10. The casting mold of claim 1 wherein the chamber is located near thesprue.
 11. The casting mold of claim 1 further comprising at least onefilter located adjacent to the chamber.
 12. The casting mold of claim 11wherein the at least one filter is a silicon carbide coated ceramic foamfilter.
 13. The casting mold of claim 1 further comprising means forcontrolling the flow of molten metal through the chamber.
 14. Thecasting mold of claim 1 comprising a plurality of chambers locatedwithin the runner system, each containing at least one metallurgicalmodifier.
 15. The casting mold of claim 14 wherein each of the pluralityof chambers contains more than a single type of metallurgical modifier.16. The casting mold of claim 14 wherein each of the plurality ofchambers contains a different metallurgical modifier.
 17. The castingmold of claim 1 further comprising a plurality of mold cavities; andwherein the runner system comprises a plurality of channels with atleast one channel serving each of the plurality of mold cavities, andeach of the plurality of channels having at least one chamber containinga metallurgical modifier.
 18. A casting mold comprising: at least onemold core; a sprue; a runner system; at least one gate; and means foradjusting the chemistry of molten metal after the molten metal isintroduced into the casting mold during a casting process.
 19. A methodfor casting an article comprising: providing a casting mold comprising asprue; a runner system comprising at least one channel; at least onegate; at least one mold element; and at least one chamber located withinthe runner system; disposing a metallurgical modifier within the atleast one chamber; and introducing molten metal into the casting mold.20. The method for casting an article of claim 19 further comprising:providing a metallurgical modifier selected from the group of, antimony,beryllium, boron, calcium, fluxing salts, phosphorous, silver, sodium,strontium, titanium, titanium boron, vanadium and zirconium, or acombination thereof.
 21. The method for casting an article of claim 19further comprising: providing a metallurgical modifier comprisingstrontium.
 22. The method for casting an article of claim 21 furthercomprising: providing a metallurgical modifier comprising about a 3% toabout a 15% strontium-containing alloy in the form of stock material.23. The method for casting an article of claim 19 further comprising:locating the chamber near the at least one gate.
 24. The method forcasting an article of claim 19 further comprising: locating the chambernear the sprue.
 25. The method for casting an article of claim 19further comprising: providing at least one filter; disposing the filteradjacent to the chamber.
 26. The method for casting an article of claim19 further comprising: providing at least one silicon carbide coatedceramic foam filter; disposing the filter adjacent to the chamber. 27.The method for casting an article of claim 19 further comprising:providing a casting mold having a plurality of chambers located withinthe runner system; disposing at least one metallurgical modifier in eachof the plurality of chambers.
 28. The method for casting an article ofclaim 27 further comprising: disposing more than a single type ofmetallurgical modifier in each of the plurality of chambers.
 29. Themethod for casting an article of claim 27 further comprising: disposingmore than a different metallurgical modifier in each of the plurality ofchambers.
 30. The method for casting an article of claim 19 furthercomprising: providing a casting mold comprising a plurality of moldcavities; providing a plurality of channels within the runner system, atleast one channel serving each of the plurality of mold cavities;providing at least one chamber in each of the plurality of channels;disposing at least one metallurgical modifier in each of the at leastone chamber.